Use of a photographically useful agent that has been previously incorporated in a photographic light-sensitive material and so contrived that its effect will be produced at the desired appropriate time involves various features different from those involved when using such an agent by addition to a processing solution. Specific examples of the features in the former case are as follows: The incorporation in a photographic light-sensitive material enables effective utilization of photographic agents of the kind which tend to decompose under the acid alkaline or oxidation reduction conditions, and consequently, can not withstand the long-term storage in a processing bath and at the same time, makes it possible to simplify the composition of a processing solution to be employed associated therewith, thereby facilitating the preparation of the processing solution. Further, this makes it possible to force a required photographic agent to function at a desired time during the photographic processing, or at only a desired place, that is, in only a specified layer and the neighboring layers of a multilayer photographic light-sensitive material. Furthermore, this permits the presence of a photographic agent in the photographic light-sensitive material in such an amount as to vary as a function of silver halide development. However, if a photographic agent is added to a photographic light-sensitive material in its active form, it becomes impossible to make the photographic agent exhibit its ability to the expected degree, because during storage before photographic processing it reacts with other components contained in the photographic light-sensitive material, or it is decomposed by heat, oxygen, etc. One method for solving the above-described problem involves adding a photographic agent to a photographic light-sensitive material in such a form that its active group is blocked and turned photographically inactive, that is, in a form of its precursor. Such a method can have various advantages in various cases to which it is applicable. For instance, in the case where the useful photographic agent is a dye, blocking a functional group of the dye which has a great effect on its spectral adsorption characteristic results in a shift of its spectral absorption band to shorter wavelengths or to longer wavelengths, and therefore, even if the dye is present in a silver halide emulsion layer having the spectral sensitivity in the wavelength region corresponding to the absorption band which the dye has in the unblocked state, a lowering of the sensitivity due to the so-called filter effect can be prevented. In another case, where the useful photographic agent is an antifoggant or a development restrainer, blocking of their active groups makes it possible to suppress desensitization arising from adsorption of these agents to light-sensitive silver halide grains and formation of silver salts upon storage and at the same time, release of these agents at required times permits the reduction of fog density without being attended by a decrease in the sensitivity, the prevention of fog due to overdevelopment, development stoppage at a desired time, and so on. In still another case, where the useful photographic agent is a developing agent, an auxiliary developing agent or a fogging agent, if their active or adsorptive groups are blocked, various photographically adverse effects which arise from semiquinones and oxidants produced by aerial oxidation upon storage can be prevented, and generation of fogging nuclei upon storage can also be prevented because injection of electrons into silver halide grains can be inhibited. Therefore, stable processing can be effected therein. In a further case that the useful photographic agent is a bleach accelerating agent or a bleach-fix accelerating agent, it becomes also possible to prevent reactions with other components copresent in the photographic light-sensitive material from occurring upon storage by blocking its active group and that, to make its expected ability bring into full play at a desired time by removing the blocking group.
As described above, a precursor of a photographic agent can be utilized as an extremely valuable tool in bringing out abilities of the photographic agent to the best advantage. However, the precursor must satisfy very severe requirements for the purpose of practical use. That is, it must be one which can satisfy two requirements contradictory to each other; one consists in ensuring stable presence of the precursor under storage conditions, and the other consists in setting its blocking group loose at a desired time during processing and in releasing the photographic agent rapidly and efficiently.
A number of techniques for blocking a photographic agent have already been known. For instance, a technique using a blocking group such as an acyl group, a sulfonyl group or the like is described in U.S. Pat. No. 3,615,617; a technique which utilizes such blocking groups as to release a photographic agent by the so-called reversal Michael reaction is described in U.S. Pat. Nos. 3,674,478, 3,791,830, and 4,009,029; a technique which utilizes such a blocking group as to release a photographic agent with the production of quinone methide or its analogs by intramolecular electron transfer is described in U.S. Pat. Nos. 3,674,478, 4,416,977, 4,420,554, and Japanese Patent Publication (unexamined) Nos. 1139/83 and 1140/83; a technique which utilizes an intramolecular ring-closing reaction is described in U.S. Pat. No. 4,310,612; a technique which utilizes cleavage of a 5-membered or 6-membered ring is described in U.S. Pat. Nos. 4,335,200 and 4,350,752, and Japanese Patent Publication (unexamined) No. 179842/82; and so on. However, these photographic agents blocked with known blocking groups suffer defects; for example, although stable under storage conditions, some precursors require a high alkaline condition such as pH higher than 12 for the processing because the photographic agent-releasing rate thereof is too slow; other precursors decompose gradually to cause a failure of its function when maintained under storage conditions, even though it can release the photographic agent at a sufficiently fast rate by the processing under mild conditions such as using a processing solution of the pH range 9 to 11; and so on.